1. Field of the Invention
The present invention relates to a hydraulic control device for a transmission capable of controlling plural kinds of controlled objects by means of one switching valve.
2. Description of the Related Art
Heretofore, in a transmission for a vehicle, shift control of the transmission is carried out by switching power transmission routes for transmitting driving force from a driving source (engine) to drive wheels using friction clutches (frictional engagement elements), brake, a belt or a chain, a dog of a synchromesh mechanism (selector device), a one-way clutch or the like, for example.
Of the elements (parts) as described above, each of the friction clutch, the brake, the belt and the chain normally carries out ON/OFF or switching control by controlling pressing power (suppress strength) of a piston or the like by hydraulic pressure. On the other hand, the dog of the synchromesh mechanism controls ON/OFF or switching control by causing its position to carry out stroke movement by means of a shift fork or the like.
Now, a so-called twin clutch transmission, capable of switching a plurality of gears by dividing a transmission system constructed by combination between two clutches and a plurality of synchromesh mechanisms into two systems and switching the two systems, has been proposed and put to practical use (for example, see Japanese Patent Application Publication No. 2007-40408 (hereinafter, referred to as “Patent Literature 1”)).
In such a twin clutch transmission, shift control is particularly carried out by controlling switching of friction clutches and synchromesh mechanisms. A hydraulic control device for a transmission carries out switching control using hydraulic pressure of hydraulic oil for controlling suppress strength, but using a flow rate of the hydraulic oil for controlling stroke movement.
Here, in the hydraulic control device for the transmission disclosed in Patent Literature 1, a solenoid valve for controlling hydraulic pressure is used to control engagement and disengagement of each clutch, and a solenoid valve for controlling a flow rate is used to control stroke of each synchromesh mechanism.
However, in the case where a solenoid valve (ON/OFF switching valve) is used in each of a clutch and a synchromesh mechanism like the hydraulic control device for the transmission disclosed in Patent Literature 1, this cases the number of components (parts) to be increased in the whole hydraulic control device. Increase in the number of components causes not only cost increase in the hydraulic control device but also cost increase in the whole vehicle. In addition, this also causes increase in weight of the hydraulic control device and the vehicle. In particular, there is a problem that these defects become apparent in the case of providing a large number of gears.